It won’t be long now.
After nearly five years of planning and construction, a team of approximately 50 workers from Traylor Brothers Construction in Evansville, IN, are putting the finishing touches on the William H. Natcher Bridge, which will connect U.S. 231/60 in Maceo, KY, (6 mi. east of Owensboro) to U.S. 231 in Rockport, IN.
“We’ve got a few more weeks of putting up the barrier wall to go. By May and June, we should be putting a latex concrete overlay on top of the existing precast road panels we have down now,” said David McDowell, resident engineer for the Kentucky Department of Transportation, and head of the Natcher Bridge Project. “Then we’re planning to paint the bridge gray, and by July we should be grouting the cables with concrete to fill any gaps inside the cable. This will help keep the cables from whipping in the wind.”
And after that? Celebrating the grand opening in August. McDowell said he knows an event is being planned by the state, but so far, there are no details.
Though some thought the bridge would be completed this time last year, McDowell claims there were no appreciable delays in the project. “We had 630 working days to get this project done, and we still have 120 left. So really, we’re right on schedule,” he said. “We had some issues with the wind, but really no real problems with the weather.”
The 4,500-ft. (1,372 m) long bridge design is one of the only cable-stayed bridges in the state, with two A-frame towers, three water piers, 10 land piers and two abutments where specially designed rotation-resistant beams come to rest. There are four lanes on the bridge, two northbound and two southbound. As part of the project, route U.S. 60 was rebuilt for about 10 mi. (16.1 km) leading up to the bridge using four lane asphalt. U.S. 231, on the other side, was widened to four lanes for approximately 1 mi. (1.6 km), going back down to two newly constructed lanes for another 4 mi. (6.4 km). This part of the project is already complete, McDowell said.
The process to erect the bridge was far more complex than a standard truss or girder bridge, he said. “When you’ve got a bridge this long, though, going the cable stayed route tends to be the most economical. That’s certainly what the cost analysis showed, and the federal government seems to be favoring this kind of construction now,” he noted.
The crew used a barge-mounted drilling rig to put 8-ft. (2.4 m) diameter shafts approximately 140 ft. (43 m) underground, into bedrock. Flight augers and cleanout buckets were used to help manage the water; and a vibratory hammer drove casings into the shafts. Rebar cages provided the shell for the shaft’s concrete centers.
“The drilling part was really our only glitch. We ended up having to switch from recirculation drills to the augers and buckets. The rock in the Owensboro area is pretty soft and full of water. We were having problems with it clogging up the machine, because the rock was too heavy for the recirculating air to push it out. So the conventional tools ended up doing a better job,” McDowell said.
Most of the erection process is done over water. More coordination than usual with the coast guard and local barge companies was needed, he added.
Two Manitowoc tower cranes, with a 360-ft. (110 m) extension and two ringer cranes with a 350-ton (317 t) load, were used in the project. First the towers were erected over top of the concrete “piles,” and two cranes were used to lift each of the 70-ft. (21 m) long girder sections into place.
Cables, ranging in size from 250 to 600 ft. (76 to 183 m) long, were pulled into precise order by an engine and pulley system, and attached to the towers and edge girders to complete the bridge’s structural steel frame. The project is based on a balanced cantilever construction design.
The bridge design work, completed by Parsons Brinckerhoff, of Louisville and New York, was heavily reliant on the aid of computers.
“Of course everything is done by AutoCAD these days, but in the case of bridge like this, you really have to rely on the computer to calculate the correct load on each of the cables, and prevent cable rotation. They also adjust to the climate conditions in the area and build in compensation for things like earthquakes and high winds. It would be darn near impossible to do that by hand,” McDowell said.
At the project’s peak, McDowell said 80 to 100 crew members were working on the bridge. Now the number of workers has whittled down to 40 to 50 as they go down the home stretch of the job. While the state has managed the project’s construction and paid for a portion of the cost, most of the money for the $75-million Natcher Bridge Project has come from federal highway funds.
Subcontractors to the project include:
• B&B Electric, of Evansville, IN, and Lexington, KY, for roadway and tower lighting;
• J&B Rebar of Cincinnati, OH;
• IMI Concrete of Rockport and Owensboro, KY;
• Vincennes Steel, of Vincennes, IN, for all structural steel; and
• Harper Industries of Shelbyville, TN, for the barrier wall slip-forms.
When complete, the new bridge promises to bring a wealth of new benefits to the communities it serves. “The Old River Bridge going into downtown gets very congested, particularly during rush hour,” McDowell said. “Having this bridge will allow large trucks to travel across our area without worsening our traffic downtown, and it should help foster new business.”
